I’m going to hazard a guess that when the TV’s speakers are playing, it is playing the ‘stereo’ track, when the Arc is playing, it’s playing either Dolby Digital, Dolby Digital Plus, or Dolby Atmos. It suggests that there’s something going on in the TV that’s trying to process the signal before sending it to the Sonos. I’d be looking at the TV’s audio settings and looking for something like ‘pass-through’ or the like. Essentially, the TV needs to not be doing any attempt at sound processing, other than reflecting what is coming in onto the ARC channel. 

These are the only sound settings I have. Am I correct on having it on multichannel(bypass).

If I select multichannel it gives me an option to switch on/off a digital out delay which I can then adjust. 

So,  based on what I see, I would definitely have it set on MultiChannel (bypass). I would expect that that setting would disable the Digital Out Offset, as it should. The less processing of the audio signal by the TV set, the better.

Just to be sure here, you are using an HDMI ARC port on the TV to connect to the Arc, and not the optical adapter, correct?

Unfortunately, I don’t own this TV so I can’t do any testing. 

Yes It is in a hdmi arc port. Could it have anything to do with the mkv files, some play with no sync issues and others don't. 

Not my area of expertise, but it’s certainly possible. Playing files from a hard drive directly to a TV/Sonos setup is non-standard. And since you say it affects ‘certain files’, it would lend credence to that thought. 

Do you have any tips to use the audio delay feature on the app. I feel like is would be easier if you could tap the + or - instead of sliding it with finger 

I have just played a TV show that was playing in sync on Friday but now it isn't. I had disconnected the arc from the TV yesterday to mount the TV to the wall, could that have anything to do with it. 

Tapping on either side of the slider has helped some folks, moving it more finely than actually trying to put your finger on the slider itself. With the size of my fingers, and my general clumsiness, I often find doing the same thing on a computer where I’m using the mouse to point and click helps me.

I would think the issue has more to do with the TV set, or the signal from your hard drive, and not the Sonos. 

I have just tried connecting it with the optical lead as I read that could help but still the same. Also doing it with ps5 but alot worse. Am going to buy HDfury arcana and see if that helps.